Thermostat apparatus



lFeb. 18, 1958 F. ROSEN ETAL TI'iERMOSTAT APPARATUS Filed July 31, 1956 vla INVENTORS,

FRANK RQSEN A,T TORNEY United States Patent O THERMOSTAT APPARATUS Frank Rosen, Pittsford, N. Y., and David M.'Rosenberg, Meadville, Pa., assignors to lWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Penn- Sylvania Application `luly 31, 1956, Serial No. 601,252

Claims. (Cl. 200-138) This invention relates to a snap acting thermostatic switch for use on the exterior surface of a water heating tank or other structure.

lt is an object of this invention to preclude lost motion between a thermally responsive snap acting member and movable contacts actuated thereby in a switch of the above type.

Another object of this invention is to minimize the change in temperature calibration due to contact wear in a switch of Vthe above type.

Another object of this invention is to provide in a switch of this type, an improved linkage between a snap acting thermally responsive member and actuating members for a pair of switches, the switches being disposed in a chamber separated from the snap acting member.

One form of thermostat made in accordance with this invention may comprise a pair of switches mounted in a switch chamber, each switch including a relatively stationary contact and a movable contact carried by the free end of an elongated cantilevered springarm. The spring arms of the switches are actuated bya snap acting bimetal member disposed outside of the switching chamber and connected thereto by means of an electrically insulating link. ln accordance with the invention, one end of the link is fastened to the bimetal member in a novel manner to preclude lost motion therebetween and the other end of the link engages each of the spring arms at a point located between the xed end of the arm and the movable contact thereon. The arms are biased toward each other to grip and position the link relative the bimetal member.

rl`he foregoing and other objects are eiected by the invention as will be apparentfrom the following description and claims taken in connection with ,the accompanying drawing, forming a part of this application, in which:

Fig. 1 is a front elevation of a thermostatic switch supported on a vertical wall of aliquid `heating tank, only a portion of the tank wall being shown;

Fig. 2 is a vertical section of the thermostatic switch taken on line ll-II of Figs. 3 and 4;

Fig. 3 is a vertical section taken on line III-III of Fig. 2;

Fig. 4 is a horizontal section Vtaken on line IV-IV of Fig. 2;

Fig. 5 is a perspective view showing the major components of the switch shown in Fig. 2 with the base and casing cut away;

Fig. 6 is a perspective View of a switch actuatinglinkage; and

Fig. 7 is a perspective view of lthe unstressed end of the snap acting bimetal before being connected to the actuating linkage in the thermostatic switch.

Referring to Fig. l, the thermostatic switch 10 is shown attached to a vertical wall 11 of a liquid heating tank. The switch comprises a preformed metal base 12 of good heat conducting material which .may be attached in any suitable manner directly to the wall 11. Supported -upon the base 12 is an insulating switch enclosing casing 13.

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Extending to the outside of the casing 13 is a temperature adjusting screw 15 to be referred to hereinafter and to which is secured an adjusting knob and pointer 14.

Referring to Figs. 2 and 4 of the drawings, the insulating casing 13 forms a switching chamber 16 having the metal base 12 as a cover and within which are supported a pair of switches 20 and 21. The base 12 has a recess 17 opening toward the tank wall within which is supported a snap acting bimetal member 24, the latter being connected to an electrically insulating link 25 extending through an opening in the base 12 and into the switching chamber 16 for actuating the switches 20 and 21. The bimetal member 24 responds to the temperature of the tank wall 11 by heat conduction through the base 12 and by direct heat radiation thereto from the wali 11.

The switch 20 comprises a movable contact 26 carried on the end of a iiat resilient spring arm 27, the other end of the arm 27 being rigidly secured to the insulating casing 13. The movable contact 26 cooperates with an adjustable contact 28 carried on the end of an adjustable spring arm 29, also supported by the insulating casing 13. The adjustable arm 29 is biased into engagement with an adjusting screw 30 threaded in the casing 13. The switch 21 comprises a movable contact 32 carried on the end of a fiat resilient spring arm 33 and co-operating with a stationary contact 34 supported by a rigid electrically conducting arm 35 carried by the casing 13. Electrically conducting rivets 37, 38, 39 and 4t) are electrically connected to the electrically conducting arms 27, 29, 33 and 35, respectively, and secure these arms to the casing 13. The rivets are electrically insulated from each other by the casing and are exposed at the exterior of the casing to form terminals that are internally threaded to receive screws for making electrical connections to the switches 2G and 21.

The spring arms 2'7 and 33 each ha e an inherent spring force which biases the contacts 25 and 32, respectively, in the directions to open switches 2% and 21. Switch 2i) is held closed against this bias in one stable position of the bimetal member 24 and switch 21 is held closed in its other stable position. The spring arms 27 and 33 extend in generally parallel planes with the contacts 26 and 32 having approximately the same line of movement. The contacts of the switches 2t) and 21 are located in one end of the chamber i6 and the arms 27 and 33 are rigidly 'supported by the casing 13 in the other end of tre chamber by means of laterally offset portions of the arms extending on opposite sides of a column 36 centrally located in the casing. The column 36 is formed integrally with casing 'i3 and encloses an internally threaded insert 41 that holds the base 12 and casing 13 together and carries the adjusting screw 15 for rotation therein. The coniiguration of arm 27 and the contact 26 thereon is identical to the arm 33 and contact 32 except that one structure has been inverted.

The connecting link 25 between the birnetal and the p switch arms 27 and 33 for actuating the latter is a flat,

electrically insulating, rigid member which may be formed of a laminated plastic or the like. One end of the link 25 is formed with cuts disposed at opposite sides thereof and slightly offset along its length to provide surfaces 42 and 43 engaging opposite faces of the bimetal 24 on opposite sides of a slot 44 in the end thereof. The slot 44, shown most clearly in Fig. 7, is widened at 45 and the link 25 is held in the widened portion. T he link is inserted edgewise into the slot 44 and then turned to the position shown in the drawings to prevent the link from moving out of the slot during operation of the thermostat. By being offset both along the length of the link and transversely relative the direction of switch actuating movement thereof, as shown in Figs. 4 and 6, the surfaces 42 and 43 stress the bimetal 24 and apply a twist to the end thereof for precluding lost motion between the birnetal and the link 25. The stress or twist of the birnetal imparted by the link is relatively slight and only just enough to preclude this lost motion without materiallyY changing'the desired snap action of the birnetal in response toltemperature changes thereof. Lost motion between the birnetal 24 and the link 25 can also be prevented by permanently bending the sides of the slot 44 in the birnetal in opposite directions without offsetting the surfaces 42 and 43 as shown in the drawings, but with such an arrangement it is more difficult to control the temperature deflection characteristics of the birnetal and, accordingly, the calibration of the thermostat.

The other end of the link 25`is cut away at one side to form a notch 46 to receive the spring arm 33 of the switch 21. An end portion 47 of the link 25 eX- tends between the arms 27 and 33. The arms 27 and 33 are biased toward the end portion 47 and are provided with rectangular openings to receive tabs 48 and 49, respectively, extending inV opposite directions from the end portion 157 to prevent transverse movement of the link 25 relative thereto. An insulating washer 50 is slipped over the tab 49 and is pivotally supported by the end portion 47 of the link 25 to provide the bearing surface for the spring arm 27. The surface 47a of the end portion 47 that is engaged by the spring 33 is flat, whereas, the surface 7b of the end portion 47 on which the washer 5@ bears is arcuate to provide pivotal support for the latter. The link 25 engages the arms 27 and 33 between their supported ends and the movable contacts. This arrangement is preferable so that a change in the limits of movement of the link made possible by wear of the contacts of switches 2@ and 21 will be minimized to reduce the change in temperature calibration of the thermostat.

The birnetal 24 is supported in a chamber formed by the recess 17 in the base 12 and the tank wall 11. The relatively stationary end of the birnetal 24 is clamped between a rigid T-shaped metal plate 51 and the T-shaped leaf spring 52. The cross bar 53 of the spring 52 is secured to the base 12 and casing 13 by a pair of rivets. The spring 52 is stressed to bias its other end into engagement with the end of the adjusting screw 15. Adjustment of the screw 15 pivots the birnetal about its relatively stationary end and changes the stresses imposed on its movable end by the link 25, thus changing the temperatures at which it will actuate the switches 2f) and 21.

The snap acting bimetal 24 is formed with three parallel legs, the outer legs 61 and 62 being crimped to reduce their length and holdrthe center leg 63 in compression to provide two positions of stability between which the free end of the birnetal member can move with a snap action in response to temperature changes. The birnetal snaps to move its free end in the direction away from the switches 2f) and 21, or to the left as seen in Fig. 2, upon an increase in temperature above a predetermined value.

The birnetal is shown in Figs. 2 and 4 in its normal or cool position in which the contacts 26 and 28 of switch 20 are in engagement. Upon heating, the lower end of the birnetal will snap to the left, as seen in Fig. 2, causing the link 25 to pull the spring arm 33 against its inherent spring force to move contact 32 into engagement with contact 34. The inherent spring'force of spring arm 27 causes the latter to follow the movement of the link 25 and thus effects contact separation in switch 20. The temperature at which the snap acting birnetal moves to open switch 2t) is dependent upon both the users adjustment of the'screw 15 and the adjustment of contact 28 which is effected by adjusting the screw 30.

The adjusting screw 30 positions Contact 28 on arm 29 relative contact 34 to adjust the differential between the temperatures at which the birnetal 24 will snap in opposite directions to open the switches 20 and 21, re-

spectively. The greater the distance that the contacts 26 and 32 can move, the greater is this differential.

After adjustment of screw 30, the Screw 15 is adjusted, while the bimetal is kept at a predetermined Calibrating temperature, until the brimetal snaps over center to separate the contacts 26 and 28 of switch 20. The adjusting knob 14 is then pressed on the knurled end of the screw 15 with the knob pointer directed to the proper indici-a on the casing 13. Thereafter, the screw 3G is cemented or otherwise secured against rotation and the 4user may adjust the screw 15 to adjust the thermostat to operate at any desired temperature Within the range indicated by the indicia on the casing.

Some applications may be found for this thermostat in which one of the two switches 2i) or 21 is not used. In this instance the unused switch contacts will not control current flow, but will act as movable and stationary abutments respectively to limit the movement of the birnetal, and the spring arm 27 or 33 of the unused switch will always preclude lost motion between the other spring arm and the link 25,

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modications without departing from the spirit thereof.

What is claimed is:

l. A thermostatic switch structure comprising a base, a switch supported on said base, a snap acting birnetal member carried by said base for actuating said switch and a rigid electrically insulating link connected lbetween a snap acting portionV of said birnetal and said switch and movable in one direction to actuate the latter, said link having integral therewith spaced surfaces for engaging opposite faces of said birnetal member, said surfaces being offset transversely relative the direction of movement of the link and disposed so as to impart a stress to the bimetal member and preclude lost motion between the latter and said link.

2. A ithermostatic switch structure comprising a base, -a switchhaving a pair of cooperating contacts supported by said base, a snap acting bimetal member carried by said base for actuating said switch, said switch including a spring arm having a fixed end and a free end carrying one of said Contacts, a rigid electrically insulating link 4connected between a snap acting portion of said birnetal and said spring arm and movable in one direction to actuate the latter, said spring arm being biased into engagement with one end of said link to prevent lost motion therebetween and said link engaging said arm intermediate the fixed and free ends thereof, the other end of said link having integral therewith spaced surfaces engaging opposite faces of the birnetal member, said surfaces being offset transversely relative said direction of movement of the link to impart a twist tothe birnetal member for precluding lost motion between the member land said link.

3. A thermostatic switch structure comprising a base, a pair of switches supported in insulated relationship on the base, a snap acting birnetal member carried by said base for actuating the switches, each of said switches having a pair of cooperating contacts and a spring arm having one end fixed to the base and a free end movably supporting one of said contacts, an insulating link connected between a snap acting portion of said birnetal and each of said spring arms to actuate the latter, said link being iiat and having a portion cut away at one side thereof to receive one of said spring arms, said link engaging each of said arms at a point intermediate the fixed and free ends thereof, said spring arms being biased in opposite `directions into engagement with spaced portions of said link, said birnetal member having a slot in said snap acting portion for securing the link thereto, the link having cuts formed at opposite edges thereof to provide surfaces for engaging opposite faces of said bimetal member'on opposite sides of said slot, said surfaces being Offset in the direction of snap acting movement of said member to impart a supporting one of said contacts, the other contact of each of said switches being so located that said spring arm biases `said movable contacts in switch opening direction, an insulating link connected between a snap acting portion of said bimetal and each of said spring arms to actuate the latter, said bimetal member being arranged to i hold one of said switches closed in each or' its stable positions, said link being at and having a portion cut away at one side thereof to receive one of said spring arms, said link engaging each of said arms at a point intermediate the fixed and free ends thereof, said spring arms being biased in opposite directions into engagement with spaced portions of said link, the other end of said link being connected to said bimetal member.

5. A thermostatic switch 'structure comprising a base, a pair of switches supported in insulated relationship on said base, a snap acting bimetal member carried by said base and movable between two stable positions for actuating said switches, each of said switches having a pair of cooperating contacts and a spring arm having one end fixed to said base and a free end movably supporting one of said contacts, the other contacts of the switches being so located that the spring arms bias their respective movable contacts in switch opening direction, an insulating link connected between a snap acting portion of said bimetal and each of said spring yarms to actuate the latter, said bimetal member being arranged to hold one of said switches closed in each of its stable positions, said link being flat and having a portion cut away at one side near one end thereof to receive one of said spring arms, said link engaging each of said arms at a point intermediate the iixed and free ends thereof, said spring arms being biased in opposite directions into engagement with spaced portions of said link, said bimetal member having a slot in said snap acting portion for securing the link thereto, the link being cut away at opposite edges thereof to provide surfaces for engaging opposite faces of said bimetal member on opposite sides of said slot, said surfaces being oset in the direction of snap `acting movement of said member to impart a twist thereto, thereby precluding lost motion between the member and said link.

References Cited in the le of this patent UNITED STATES PATENTS 2,487,276 Shewmon et a1 Nov. 8, 1949 2,655,621 Lee Oct. 13, 1953 2,715,167 Mettler Aug. 9, 1955 

